In conventional systems, a vehicle is prevented from departing from its current lane of travel, for example, by determining whether there is a possibility that the vehicle will depart from the lane, and activating a steering actuator if there is such a possibility, thereby providing assisted steering power in a direction to avoid lane departure.
In addition, in conventional technology, a vehicle is prevented from departing from a lane by controlling a braking power actuator on the basis of a certain amount of lateral displacement of the vehicle from its previous position of travel, to provide braking power to the wheel(s) on the side of the vehicle opposite to the direction of lane departure.
Generally, in such a vehicle departure prevention system, when it is to be determined whether the vehicle is tending to depart from the lane of travel, a judgment is made based on whether the vehicle will depart from the lane in the near future, such as after the lapse of a predetermined period of time. Here, it may be regarded that a vehicle departs from a lane if all the wheels of the vehicle are outside the lane. Therefore, a vehicle may be tending to depart from the lane even when at least one of left and right side wheels crosses the lane unless all the wheels are outside the lane.
As a result, for example, when the yaw angle of the vehicle is large with respect to the lane of travel, the control operation for avoiding departure from the lane may be performed at a time when the vehicle is positioned well inside the lane marker position;, that is, in the vicinity of the center of the lane of travel. (The “yaw angle” is defined as the angle between the direction of travel of the vehicle and the direction of the lane.) Accordingly, the area in the lane in which the driver can freely steer the vehicle without the control operating to avoid departure from the lane becomes narrower as the width of the lane becomes smaller, so that in some cases, the driver may feel the control operation is performed prematurely.
The present lane departure prevention system does not make the driver feel the controlling operation is premature, regardless of the yaw angle, and so it does not discomfort the driver.
The present lane departure prevention system monitors whether a vehicle is tending to depart from the lane of travel based on current lateral displacement of the vehicle relative to the lane of travel, which is detected by a traveling status detecting unit. When it is determined that the vehicle is tending to depart from the lane of travel, the system allows a departure avoidance control unit to control motion of the vehicle to avoid the lane departure. The degree to which vehicle motion is controlled by the departure avoidance control is calculated based on the current yaw angle.
The present lane departure prevention system does not determine that the vehicle is tending to depart from the lane until the amount of lateral displacement reaches a predetermined value, and so it is possible to prevent the driver from feeling that the controlling operation is premature. In addition, since the degree to which the vehicle is to be controlled by the departure avoidance control is calculated based on the current yaw angle when it is determined that the vehicle is tending to depart from the lane of travel, it is possible to obtain a control effect by the departure avoidance control by, for example, estimating a future departure status of the vehicle from the lane of travel based on the current yaw angle and calculating the degree of control based on the estimated future lane departure status.